Wednesday, December 10, 2014

Fabrics, Dyes and Mordants


In December we looked at mordants, chemicals which help dyes bind to fabrics.  We prepared some natural dyes from turmeric, cochineal, onion skins, walnut shells and hulls, and beetroot. Our fabric samples were cotton, wool, linen, silk, and acetate. We discussed where these fabrics come from - plant, animal or synthetic. The mordants we compared were Alum (potassium aluminium sulphate), salt water, and a control of plain water. 

The mordant forms a bond with both the fabric and the dye - as Lachlan said, it acts like double-sided sticky tape. The buckets contain fabric samples which have soaked for several days in solutions of two different Mordants - alum (potassium aluminium sulphate) and salt (Sodium chloride). A control set of fabric samples soaked in tap water. We prepared some natural dyes from cochineal larvae, onion skins, beetroot, walnut husks and shells, and turmeric. Our fabrics were silk, cotton, linen, wool and acetate. We heated the fabrics in the dye, then rinsed them and compared the results in terms of depth of colour.





















Friday, October 10, 2014

Displacement Reactions

We did lots of displacement tests. Photos to come for the copper sulphate etc, but in the meantime these were good:

Thursday, October 9, 2014

Oxides and Carbonates


We did several practical activities from the Royal Society of Chemistry’s Classic Chemistry Experiments collection today, to illustrate important chemical reactions. We often hear the terms ‘carbonate’ and 'oxide’ so today we found out a bit more about what these mean.  A carbonate of a metal has a CO3 attached to it, while an oxide has oxygen attached to it.

The Combustion of Iron Wool

We made a seesaw balance by perching strips of wood on triangular blocks.  We put plasticine at one end and iron wool at the other, arranged so that the plasticine just outweighed the iron wool.  We set light to the iron wool and waited for something interesting to happen.  It was quite difficult to set alight and, when we did set it alight, most of us didn’t get a conclusive result.  We tried again, using a longer balance beam - a metal metre rule.  This worked brilliantly and we saw that,, even though sparks were coming off the burning iron wool, it still tipped the balance away from the plasticine and moved down.  This showed that the iron wool became heavier as it burned.
The RSC description and instructions for this : The Combusion of Iron Wool

The Change in Mass when Magnesium Burns

A short piece of magnesium ribbon was cleaned and placed in a ceramic crucible with a lid. The crucible was weighed and the mass noted. The crucible was placed on a pipe clay triangle, on top of a tripod, over a bunsen burner.  We heated it strongly and lifted the lid to let more air in.  We could see a bright light coming from inside the crucible.  After it had all cooled down, we weighed it again and it weighed slightly more than it had originally. The magnesium ribbon had changed into white powder. This was magnesium oxide, and the crucible weighed more because the additional oxygen which had combined with the magnesium had increased the overall mass.
Further reading and how-to: RSC Change in mass when magnesium burns

The Effect of Heat on Metal Carbonates

We heated two different chemicals - sodium carbonate, and copper carbonate.  Each was put into a separate test tube, then we put a bung in which had a hole and a right-angled glass delivery tube.  Of particular note: Alison and Angie made these customised delivery tubes by heating plain glass tubing in a strong flame! The gas produced was bubbled through limewater, and for both chemicals the gas turned the limewater milky.  This showed it was carbon dioxide.
Further info and instructions: RSC Effect of Heat on Metal Carbonates

Thursday, March 13, 2014

Chromatography

We used chromatography to investigate colourings used in sweets, and to study a ransom note.

Monday, March 10, 2014

Distillation of alchohol

Distillation of alcohol - we made a brew two sessions ago, adding yeast to water and sugar. Today we attempted to separate the alcohol from the liquid. We put the liquid in round-bottomed flasks suspended in water baths over hot plates, and attached Leibig condensers to the flasks. We didn’t use naked flames because we would be dealing with flammable vapours. We monitored the temperature to keep it ideally around 78C - 80C. As before, we put iced water in the condensers. It was hard to get the setup right, but we produced a few drops of condensate which smelled of alcohol.